Until now, as a reproducing magnetic head for high density magnetic recording, a magnetic head (MR head) using a magneto-resistance effect element (hereinafter referred to as MR element) is under study. At present time, for a magneto-resistance effect film (MR film), Ni.sub.80 Fe.sub.20 (atomic %) alloy (permalloy) or the like, which shows anisotropic magneto-resistance effect (AMR), is generally used. Since the AMR film possesses such a small magneto-resistance change rate as about 3% (MR change rate), as an alternative material for the magneto-resistance effect film material, an artificial lattice film and a spin valve film such as (Co/Cu)n and the like, which display giant magneto-resistance effect (GMR), are attracting attention.
In an MR element using an AMR film, since the AMR film possesses magnetic domains, Barkhausen noise resulting from the existence of the magnetic domains becomes a drawback when putting to practical use. Therefore, various means for making an AMR film into a single domain are being studied. As one method among them, there is a method in which the magnetic domains in an AMR film is controlled in one particular direction by utilizing exchange coupling between an AMR film, which is a ferromagnetic material, and an anti-ferromagnetic material film. As an anti-ferromagnetic material in this case, .gamma.-FeMn alloy is so far well known (see the specification of U.S. Pat. No. 4,103,315, the specification of U.S. Pat. No. 5,014,147, and the specification of U.S. Pat. No. 5,315,468, for example).
Besides, a spin valve film comprises a sandwich film possessing a laminate structure formed of a ferromagnetic layer/a non-magnetic layer/a ferromagnetic layer, and, by pinning magnetization of one ferromagnetic layer, a GMR is obtained. For pinning magnetization of another ferromagnetic layer of the spin valve film, a technology utilizing exchange coupling between an anti-ferromagnetic film and a ferromagnetic film is generally used. For a constituent material of the anti-ferromagnetic material film in this case, .gamma.-FeMn alloy is generally in use.
However, .gamma.-FeMn alloy is poor in corrosion resistivity. In particular, it is easily corroded by water. Thus, since an MR element utilizing an anti-ferromagnetic material film consisting of .gamma.-FeMn alloy is easily corroded by, particularly, water in the air during processing step into an element shape or a head shape, thus, as a result of this corrosion, the exchange coupling force with an MR film tends to gradually deteriorate in time.
For an exchange coupling film formed between an anti-ferromagnetic material film and a ferromagnetic material film, from reliability view-point, an exchange coupling force is required to be 200 Oe and more at, for example, 393 K. To realize an exchange coupling force of 200 Oe and more at 393 K, in addition to an exchange coupling force at room temperature, temperature dependency of the exchange coupling force is required to be good. Concerning the temperature dependency of the exchange coupling force, a blocking temperature at which temperature the exchange coupling force between a ferromagnetic material film and an anti-ferromagnetic material film is lost is desirable to be high as much as possible. However, .gamma.-FeMn alloy is as low as 443 K in the blocking temperature, and also the temperature dependency of the exchange coupling force thereof is very poor.
Besides, in U.S. Pat. No. 5315468 for example, .theta.-Mn alloy, such as NiMn alloy, possessing a crystal structure of face-centered tetragonal crystal system is described as an anti-ferromagnetic material film. When an anti-ferromagnetic material film consisting of the .theta.-Mn alloy is used, it is shown that the exchange coupling force between the anti-ferromagnetic material film and the ferromagnetic material film does not deteriorate.
Further, as an anti-ferromagnetic material film high in a blocking temperature, large in an exchange coupling force, and excellent in corrosion resistivity, IrMn alloy possessing a crystal structure of face-centered tetragonal crystal system is proposed. As anti-ferromagnetic material films possessing the same crystal structure, .gamma.-Mn alloy such as PtMn alloy or RhMn alloy other than .gamma.-FeMn alloy is known (see U.S. Pat. No. 4,103,315, U.S. Pat. No. 5,315,468).
As described above, Mn alloys such as IrMn alloy, PtMn alloy, RhMn alloy, NiMn alloy, PdMn alloy, and CrMn alloy are excellent in corrosion resistivity and further can be enhanced in the blocking temperature of the exchange coupling film. Thus, they are attracting attention as an anti-ferromagnetic material capable of enhancing long term reliability of the MR element.
Now, as a method for forming an anti-ferromagnetic material film, the sputtering method is generally used. Using a sputtering target comprising each element which constitutes the above described Mn alloys, an anti-ferromagnetic material film is formed into a film by a sputtering method. However, an anti-ferromagnetic material film formed into a film with a conventional sputtering target tends to form a nonhomogeneous film composition in a formed film plane. In such an exchange coupling film formed between an anti-ferromagnetic material film and a ferromagnetic material film, there is a problem that a sufficient exchange coupling force can not be obtained. In addition, there is another problem that an MR element and an MR head which use such an exchange coupling film tend to be adversely affected on the anti-ferromagnetic material film from the other constituent films to deteriorate in its exchange coupling performance.
Further, the conventional sputtering target tends to cause a large composition deviation between film composition sputtered at the initial stage of sputtering and that obtained at the life end. Such a temporal change of the film composition of the anti-ferromagnetic material film can also cause to deteriorate the exchange coupling performance.
The first object of the present invention is to stabilize a film composition and a film quality of an anti-ferromagnetic material film comprising a Mn alloy excellent in corrosion resistivity and thermal property, and to provide a sputtering target less in the composition deviation up to the life end. The second object of the present invention is to provide a sputtering target capable of forming with reproducibility an anti-ferromagnetic material film of which exchange coupling force at the room temperature and high temperature region is stable, and to provide an anti-ferromagnetic material film possessing such performance. The third object of the present invention is, by using an anti-ferromagnetic material film excellent in such performance, to provide a magneto-resistance effect element which enables to obtain stable performance and stable output power with reproducibility.